Optical information recording device and method, optical information reproducing device and method, and optical information recording/reproducing device and method

ABSTRACT

An object of the present invention is to record and reproduce information through the use of holography, and achieve compact configuration of an optical system with no reduction in the amount of information. For recording, a spatial light modulator ( 25 ) generates information light and a phase spatial light modulator ( 17 ) generates recording-specific reference light having a spatially modulated phase. The information light and the recording-specific reference light are projected onto one side of an information recording layer ( 3 ) of an optical information recording medium ( 1 ) coaxially so as to converge on a reflecting surface. At the time of recording of information, P-polarized recording-specific reference light and S-polarized information light are each optically rotated by a two-way split optical rotation plate ( 21 ) in directions different between respective half areas of the cross section of the beam thereof. An interference pattern resulting from interference between the information light yet to impinge on the reflecting surface and the recording-specific reference light reflected by the reflecting surface and an interference pattern resulting from interference between the recording-specific reference light yet to impinge on the reflecting surface and the information light reflected by the reflecting surface are recorded in the information recording layer ( 3 ).

TECHNICAL FIELD

[0001] The present invention relates to an optical information recordingapparatus and method for recording information on an optical informationrecording medium through the use of holography, an optical informationreproducing apparatus and method for reproducing information from anoptical information recording medium through the use of holography, andan optical information recording/reproducing apparatus and method forrecording information on an optical information recording medium andreproducing the information from the optical information recordingmedium through the use of holography.

BACKGROUND ART

[0002] In general, holographic recording for recording information in arecording medium through the use of holography is performed bysuperimposing light that carries image information on reference lightwithin the recording medium and by writing a resultingly generatedinterference pattern into the recording medium. For reproducing theinformation recorded, the recording medium is irradiated with referencelight such that the image information is reproduced through diffractionderived from the interference pattern.

[0003] In recent years, volume holography, or digital volume holographyin particular, has been developed and is attracting attention inpractical fields for ultra-high density optical recording. Volumeholography is a method for writing a three-dimensional interferencepattern by making positive use of a recording medium in a direction ofits thickness as well, and is characterized in that it is possible toenhance the diffraction efficiency by increasing the thickness of themedium, and a greater recording capacity can be achieved by employingmultiplex recording. Digital volume holography is a computer-orientedholographic recording method which uses the same recording medium andrecording method as with the volume holography, whereas the imageinformation to be recorded is limited to binary digital patterns. In thedigital volume holography, analog image information such as a picture isonce digitized and developed into two-dimensional digital patterninformation, and then it is recorded as image information. Forreproduction, this digital pattern information is read and decoded torestore the original image information for display. Consequently, evenif the signal-to-noise ratio (hereinafter referred to as SN ratio)during reproduction is somewhat poor, it is possible reproduce theoriginal information with extremely high fidelity by performingdifferential detection and/or error correction on the binary dataencoded.

[0004] Conventional optical information recording/reproducing methodsthat use holography have had a problem that the reproduced informationdeteriorates in SN ratio if reproduction-specific reference light isalso incident on a photodetector for detecting reproduction light. Forthat reason, in the conventional optical informationrecording/reproducing methods, information light and recording-specificreference light are often allowed to be incident on the recording mediumwith a predetermined angle therebetween at the time of recording, sothat reproduction light and reproduction-specific reference light can bespatially separated from each other at the time of reproduction.Consequently, the reproduction light, which occurs at the time ofreproduction, travels at a predetermined angle with respect to thereproduction-specific reference light. This allows the reproductionlight and the reproduction-specific reference light to be spatiallyseparated from each other.

[0005] Nevertheless, when the information light and therecording-specific reference light are allowed to be incident on therecording medium with a predetermined angle therebetween at the time ofrecording so as to spatially separate the reproduction light and thereproduction-specific reference light from each other at the time ofreproduction as described above, there arises a problem that the opticalsystem for recording and reproduction becomes greater in size.

[0006] Published Unexamined Japanese Patent Application (KOKAI) Heisei10-124872 discloses a technique of recording an interference patternobtained between information light and reference light in an informationrecording layer in which information is recorded through the use ofholography, by irradiating the information recording layer with theinformation light and the reference light on the same side thereof suchthat they converge at different positions in the direction of thicknessof the information recording layer.

[0007] This technique, however, has a problem that a special opticalsystem is required for allowing the information light and the referencelight to converge at different positions.

[0008] Published Unexamined Japanese Patent Application (KOKAI) Heisei10-124872 mentioned above also discloses a technique in which a part ofthe cross section of the beam to be projected onto the recording mediumis spatially modulated to form information light while reference lightis formed of the other part of the cross section of the beam, and aninterference pattern obtained therebetween is recorded in theinformation recording layer. In this technique, a recording medium isused which has a reflecting surface on a side of the informationrecording layer opposite to the side to be irradiated with theinformation light and the reference light, so that an interferencepattern obtained between the information light yet to impinge on thereflecting surface and the reference light reflected by the reflectingsurface and an interference pattern obtained between the reference lightyet to impinge on the reflecting surface and the information lightreflected by the reflecting surface are recorded in the informationrecording layer.

[0009] This technique, however, has a problem that the amount ofinformation recordable is reduced because information can be carried byonly a part of the cross section of the beam projected onto therecording medium.

DISCLOSURE OF THE INVENTION

[0010] It is an object of the invention to provide an opticalinformation recording apparatus and method, an optical informationreproducing apparatus and method, and an optical informationrecording/reproducing apparatus and method for recording or reproducinginformation through the use of holography, which allow a smallconfiguration of the optical system for recording or reproductionwithout causing a reduction in the amount of information.

[0011] An optical information recording apparatus of the invention is anapparatus for recording information in an optical information recordingmedium having an information recording layer in which information isrecorded through the use of holography and one side of which isirradiated with light for recording or reproducing information, and areflecting surface disposed on the other side of the informationrecording layer, the apparatus comprising:

[0012] information light generation means for generating informationlight that carries information;

[0013] recording-specific reference light generation means forgenerating recording-specific reference light; and

[0014] a recording optical system for irradiating the informationrecording layer with the information light generated by the informationlight generation means and the recording-specific reference lightgenerated by the recording-specific reference light generation meanssuch that the information is recorded in the information recording layerin the form of an interference pattern resulting from interferencebetween the information light and the recording-specific referencelight, wherein

[0015] the recording optical system projects the information light andthe recording-specific reference light coaxially onto the one side ofthe information recording layer such that they converge on thereflecting surface, and

[0016] the recording optical system causes each of the information lightand the recording-specific reference light to have directions ofpolarization that are different between respective half areas of a crosssection of a beam thereof such that the direction of polarization of theinformation light yet to impinge on the reflecting surface coincideswith that of the recording-specific reference light reflected by thereflecting surface, and the direction of polarization of therecording-specific reference light yet to impinge on the reflectingsurface coincides with that of the information light reflected by thereflecting surface.

[0017] An optical information recording method is a method for recordinginformation in an optical information recording medium having aninformation recording layer in which information is recorded through theuse of holography and one side of which is irradiated with light forrecording or reproducing information, and a reflecting surface disposedon the other side of the information recording layer, the methodcomprising:

[0018] the step of generating information light that carriesinformation;

[0019] the step of generating recording-specific reference light; and

[0020] the recording step in which the information recording layer isirradiated with the information light and the recording-specificreference light such that the information is recorded in the informationrecording layer in the form of an interference pattern resulting frominterference between the information light and the recording-specificreference light, wherein

[0021] in the recording step, the information light and therecording-specific reference light are projected coaxially onto the oneside of the information recording layer such that they converge on thereflecting surface, and

[0022] in the recording step, each of the information light and therecording-specific reference light is made to have directions ofpolarization that are different between respective half areas of a crosssection of a beam thereof such that the direction of polarization of theinformation light yet to impinge on the reflecting surface coincideswith that of the recording-specific reference light reflected by thereflecting surface, and the direction of polarization of therecording-specific reference light yet to impinge on the reflectingsurface coincides with that of the information light reflected by thereflecting surface.

[0023] According to the optical information recording apparatus or theoptical information recording method of the invention, the informationlight and the recording-specific reference light are projected coaxiallyonto the one side of the information recording layer such that theyconverge on the reflecting surface. In the optical information recordinglayer, the direction of polarization of the information light yet toimpinge on the reflecting surface coincides with that of therecording-specific reference light reflected by the reflecting surface,so that an interference pattern resulting from interference therebetweenis recorded. On the other hand, the direction of polarization of therecording-specific reference light yet to impinge on the reflectingsurface coincides with that of the information light reflected by thereflecting surface, so that an interference pattern resulting frominterference therebetween is recorded.

[0024] In the optical information recording apparatus of the invention,the recording optical system may have optical rotation means foroptically rotating light passing therethrough in directions differentbetween the respective areas, and may optically rotate, with the opticalrotation means, each of the recording-specific reference light having apredetermined first direction of polarization and the information lighthaving a second direction of polarization different from the firstdirection of polarization to make the directions of polarizationdifferent between the respective areas.

[0025] In the optical information recording apparatus of the invention,the recording-specific reference light generation means may generaterecording-specific reference light having a spatially modulated phase.In this case, the recording-specific reference light may have such amodulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of an optical axis of the opticalsystem for irradiating the information recording layer with therecording-specific reference light is not the same as the modulationpattern.

[0026] In the optical information recording method of the invention, inthe recording step, each of the recording-specific reference lighthaving a predetermined first direction of polarization and theinformation light having a second direction of polarization differentfrom the first direction of polarization may be optically rotated indirections different between the respective areas to make the directionsof polarization different between the respective areas.

[0027] In the optical information recording method of the invention, thestep of generating recording-specific reference light may generaterecording-specific reference light having a spatially modulated phase.In this case, the recording-specific reference light may have such amodulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of an optical axis of the opticalsystem for irradiating the information recording layer with therecording-specific reference light is not the same as the modulationpattern.

[0028] An optical information reproducing apparatus of the invention isan apparatus for reproducing information through the use of holographyfrom an optical information recording medium having an informationrecording layer in which information is recorded through the use ofholography and one side of which is irradiated with light for recordingor reproducing information, and a reflecting surface disposed on theother side of the information recording layer, the information beingrecorded in the information recording layer based on information lightand recording-specific reference light that are projected coaxially ontothe one side of the information recording layer such that they convergeon the reflecting surface, in the form of an interference patternresulting from interference between the information light yet to impingeon the reflecting surface and the recording-specific reference lightreflected by the reflecting surface and an interference patternresulting from interference between the recording-specific referencelight yet to impinge on the reflecting surface and the information lightreflected by the reflecting surface, the apparatus comprising:

[0029] reproduction-specific reference light generation means forgenerating reproduction-specific reference light;

[0030] a reproducing optical system for irradiating the informationrecording layer with the reproduction-specific reference light generatedby the reproduction-specific reference light generation means and forcollecting reproduction light generated at the information recordinglayer when irradiated with the reproduction-specific reference light;and

[0031] detection means for detecting the reproduction light collected bythe reproducing optical system, wherein

[0032] the reproducing optical system projects the reproduction-specificreference light onto the information recording layer to allow it toconverge on the reflecting surface, such that the irradiation with thereproduction-specific reference light and the collection of thereproduction light are performed on the one side, and that thereproduction-specific reference light and the reproduction light arearranged coaxially, and

[0033] the recording optical system has optical rotation means foroptically rotating light passing therethrough in directions differentbetween respective half areas of a cross section of the beam of thelight, and optically rotates, with the optical rotation means, thereproduction-specific reference light having a predetermined firstdirection of polarization to convert the same into reproduction-specificreference light having directions of polarization different between therespective areas to irradiate the information recording layer therewith,and optically rotates, with the optical rotation means, the reproductionlight and return light resulting from the reproduction-specificreference light reflected by the reflecting surface to convert them intoreproduction light having the first direction of polarization over anentire cross section of a beam thereof and return light having a seconddirection of polarization different from the first direction ofpolarization over an entire cross section of a beam thereof.

[0034] An optical information reproducing method of the invention is amethod for reproducing information through the use of holography from anoptical information recording medium having an information recordinglayer in which information is recorded through the use of holography andone side of which is irradiated with light for recording or reproducinginformation, and a reflecting surface disposed on the other side of theinformation recording layer, the information being recorded in theinformation recording layer based on information light andrecording-specific reference light that are projected coaxially onto theone side of the information recording layer such that they converge onthe reflecting surface, in the form of an interference pattern resultingfrom interference between the information light yet to impinge on thereflecting surface and the recording-specific reference light reflectedby the reflecting surface and an interference pattern resulting frominterference between the recording-specific reference light yet toimpinge on the reflecting surface and the information light reflected bythe reflecting surface, the method comprising:

[0035] the step of generating reproduction-specific reference light;

[0036] the reproducing step in which the information recording layer isirradiated with the reproduction-specific reference light generated bythe reproduction-specific reference light generation means, andreproduction light generated at the information recording layer whenirradiated with the reproduction-specific reference light is collected;and

[0037] the step of detecting the reproduction light, wherein

[0038] in the reproducing step, the reproduction-specific referencelight is projected onto the information recording layer so as toconverge on the reflecting surface such that the irradiation with thereproduction-specific reference light and the collection of thereproduction light are performed on the one side, and that thereproduction-specific reference light and the reproduction light arearranged coaxially, and

[0039] in the reproducing step, the reproduction-specific referencelight having a predetermined first direction of polarization isoptically rotated in directions different between respective half areasof a cross section of a beam thereof, and thereby converted intoreproduction-specific reference light having directions of polarizationdifferent between the respective areas to irradiate the informationrecording layer therewith, and the reproduction light and return lightresulting from the reproduction-specific reference light reflected bythe reflecting surface are each optically rotated in directionsdifferent between the respective areas and thereby converted intoreproduction light having the first direction of polarization over anentire cross section of a beam thereof and return light having a seconddirection of polarization different from the first direction ofpolarization over an entire cross section of a beam thereof.

[0040] In the optical information reproducing apparatus or the opticalinformation reproducing method of the invention, thereproduction-specific reference light is projected onto the informationrecording layer so as to converge on the reflecting surface. Theprojection of the reproduction-specific reference light and thecollection of the reproduction light are performed on the one side, andthe reproduction-specific reference light and the reproduction light arearranged coaxially. The reproduction-specific reference light having apredetermined first direction of polarization is optically rotated indirections different between respective half areas of a cross section ofthe beam thereof, and thereby converted into reproduction-specificreference light having directions of polarization different between therespective areas to irradiate the information recording layer therewith,and the reproduction light and the return light are each opticallyrotated in directions different between the respective areas and therebyconverted into reproduction light having the first direction ofpolarization over the entire cross section of the beam thereof andreturn light having a second direction of polarization over the entirecross section of the beam thereof.

[0041] In the optical information reproducing apparatus of theinvention, the reproducing optical system may further have polarizationseparation means for separating the reproduction light having passedthrough the optical rotation means and the return light having passedthrough the optical rotation means from each other depending on adifference in direction of polarization.

[0042] In the optical information reproducing apparatus of theinvention, the reproduction-specific reference light generation meansmay generate reproduction-specific reference light having a spatiallymodulated phase. In this case, the reproduction-specific reference lightmay have such a modulation pattern that a pattern which ispoint-symmetric to the modulation pattern about the position of anoptical axis of the optical system for irradiating the informationrecording layer with the reproduction-specific reference light is notthe same as the modulation pattern.

[0043] In the optical information reproducing method of the invention,the reproducing step may separate the reproduction light that has beenoptically rotated and the return light that has been optically rotatedfrom each other depending on a difference in direction of polarization.

[0044] In the optical information reproducing method of the invention,the step of generating reproduction-specific reference light maygenerate reproduction-specific reference light having a spatiallymodulated phase. In this case, the reproduction-specific reference lightmay have such a modulation pattern that a pattern which ispoint-symmetric to the modulation pattern about the position of anoptical axis of the optical system for irradiating the informationrecording layer with the reproduction-specific reference light is notthe same as the modulation pattern.

[0045] An optical information recording/reproducing apparatus of theinvention is an apparatus for recording information in an opticalinformation recording medium having an information recording layer inwhich information is recorded through the use of holography and one sideof which is irradiated with light for recording or reproducinginformation, and a reflecting surface disposed on the other side of theinformation recording layer, and for reproducing information from theoptical information recording medium, the apparatus comprising:

[0046] information light generation means for generating informationlight that carries information;

[0047] recording-specific reference light generation means forgenerating recording-specific reference light;

[0048] reproduction-specific reference light generation means forgenerating reproduction-specific reference light;

[0049] a recording/reproducing optical system for, to recordinformation, irradiating the information recording layer with theinformation light generated by the information light generation meansand the recording-specific reference light generated by therecording-specific reference light generation means such thatinformation is recorded in the information recording layer in the formof an interference pattern resulting from interference between theinformation light and the recording-specific reference light, and, toreproduce information, irradiating the information recording layer withthe reproduction-specific reference light generated by thereproduction-specific reference light generation means and collectingreproduction light generated at the information recording layer whenirradiated with the reproduction-specific reference light; and

[0050] detection means for detecting the reproduction light collected bythe recording/reproducing optical system, wherein

[0051] the recording/reproducing optical system has optical rotationmeans for optically rotating light passing therethrough in directionsdifferent between respective half areas of a cross section of a beam ofthe light,

[0052] to record information, the recording/reproducing optical systemprojects the information light and the recording-specific referencelight coaxially onto the one side of the information recording layersuch that they converge on the reflecting surface,

[0053] to record information, the recording/reproducing optical systemoptically rotates, with the optical rotation means, each of therecording-specific reference light having a predetermined firstdirection of polarization and the information light having a seconddirection of polarization different from the first direction ofpolarization to cause each of the information light and therecording-specific reference light to have directions of polarizationthat are different between the respective areas such that the directionof polarization of the information light yet to impinge on thereflecting surface coincides with that of the recording-specificreference light reflected by the reflecting surface, and the directionof polarization of the recording-specific reference light yet to impingeon the reflecting surface coincides with that of the information lightreflected by the reflecting surface,

[0054] to reproduce information, the recording/reproducing opticalsystem projects the reproduction-specific reference light onto theinformation recording layer to allow it to converge on the reflectingsurface, such that the irradiation with the reproduction-specificreference light and the collection of the reproduction light areperformed on the one side, and that the reproduction-specific referencelight and the reproduction light are arranged coaxially, and

[0055] to reproduce information, the recording/reproducing opticalsystem optically rotates, with the optical rotation means, thereproduction-specific reference light having the first direction ofpolarization to convert the same into reproduction-specific referencelight having directions of polarization different between the respectiveareas to irradiate the information recording layer therewith, andoptically rotates, with the optical rotation means, the reproductionlight and return light resulting from the reproduction-specificreference light reflected by the reflecting surface to convert them intoreproduction light having the first direction of polarization over anentire cross section of a beam thereof and return light having a seconddirection of polarization different from the first direction ofpolarization over an entire cross section of a beam thereof.

[0056] An optical information recording/reproducing method of theinvention is a method for recording information in an opticalinformation recording medium having an information recording layer inwhich information is recorded through the use of holography and one sideof which is irradiated with light for recording or reproducinginformation, and a reflecting surface disposed on the other side of theinformation recording layer, and for reproducing information from theoptical information recording medium, the method comprising:

[0057] the step of generating information light that carriesinformation;

[0058] the step of generating recording-specific reference light;

[0059] the recording step in which the information recording layer isirradiated with the information light and the recording-specificreference light such that the information is recorded in the informationrecording layer in the form of an interference pattern resulting frominterference between the information light and the recording-specificreference light;

[0060] the step of generating reproduction-specific reference light;

[0061] the reproducing step in which the information recording layer isirradiated with the reproduction-specific reference light, andreproduction light generated at the information recording layer whenirradiated with the reproduction-specific reference light is collected;and

[0062] the step of detecting the reproduction light, wherein

[0063] in the recording step, the information light and therecording-specific reference light are projected coaxially onto the oneside of the information recording layer such that they converge on thereflecting surface,

[0064] in the recording step, each of the recording-specific referencelight having a predetermined first direction of polarization and theinformation light having a second direction of polarization differentfrom the first direction of polarization is optically rotated indirections different between respective half areas of a cross section ofa beam thereof to cause each of the information light and therecording-specific reference light to have directions of polarizationdifferent between the respective areas such that the direction ofpolarization of the information light yet to impinge on the reflectingsurface coincides with that of the recording-specific reference lightreflected by the reflecting surface, and the direction of polarizationof the recording-specific reference light yet to impinge on thereflecting surface coincides with that of the information lightreflected by the reflecting surface,

[0065] in the reproducing step, the reproduction-specific referencelight is projected onto the information recording layer so as toconverge on the reflecting surface, such that the irradiation with thereproduction-specific reference light and the collection of thereproduction light are performed on the one side, and that thereproduction-specific reference light and the reproduction light arearranged coaxially, and

[0066] in the reproducing step, the reproduction-specific referencelight having a predetermined first direction of polarization isoptically rotated in directions different between respective half areasof a cross section of a beam thereof, and thereby converted intoreproduction-specific reference light having directions of polarizationdifferent between the respective areas to irradiate the informationrecording layer therewith, and the reproduction light and return lightresulting from the reproduction-specific reference light reflected bythe reflecting surface are each optically rotated in directionsdifferent between the respective areas and thereby converted intoreproduction light having the first direction of polarization over anentire cross section of a beam thereof and return light having a seconddirection of polarization different from the first direction ofpolarization over an entire cross section of a beam thereof.

[0067] In the optical information recording/reproducing apparatus or theoptical information recording/reproducing method of the invention, torecord information, the information light and the recording-specificreference light are projected coaxially onto one side of the informationrecording layer so as to converge on the reflecting surface. In theoptical information recording layer, the direction of polarization ofthe information light yet to impinge on the reflecting surface coincideswith that of the recording-specific reference light reflected by thereflecting surface, so that an interference pattern resulting frominterference therebetween is recorded. On the other hand, the directionof polarization of the recording-specific reference light yet to impingeon the reflecting surface coincides with that of the information lightreflected by the reflecting surface, so that an interference patternresulting from interference therebetween is recorded. To reproduceinformation, the reproduction-specific reference light is projected ontothe information recording layer so as to converge on the reflectingsurface. The projection of the reproduction-specific reference light andthe collection of the reproduction light are performed on the one side,and the reproduction-specific reference light and the reproduction lightare arranged coaxially. The reproduction-specific reference light havinga predetermined first direction of polarization is optically rotated indirections different between respective half areas of a cross section ofthe beam thereof, and thereby converted into reproduction-specificreference light having directions of polarization different between therespective areas to irradiate the information recording layer therewith,and the reproduction light and return light are each optically rotatedin directions different between the respective areas and therebyconverted into reproduction light having the first direction ofpolarization over the entire cross section of the beam thereof andreturn light having a second direction of polarization over the entirecross section of the beam thereof.

[0068] In the optical information recording/reproducing apparatus of theinvention, the recording/reproducing optical system may further havepolarization separation means for separating the reproduction lighthaving passed through the optical rotation means and the return lighthaving passed through the optical rotation means from each otherdepending on a difference in direction of polarization.

[0069] In the optical information recording/reproducing apparatus of theinvention, the recording-specific reference light generation means maygenerate recording-specific reference light having a spatially modulatedphase, and the reproduction-specific reference light generation meansmay generate reproduction-specific reference light having a spatiallymodulated phase. In this case, the recording-specific reference lightand the reproduction-specific reference light may each have such amodulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of an optical axis of the opticalsystem for irradiating the information recording layer with therecording-specific reference light and the reproduction-specificreference light is not the same as the modulation pattern.

[0070] In the optical information recording/reproducing method of theinvention, the reproducing step may separate the reproduction light thathas been optically rotated and the return light that has been opticallyrotated from each other depending on a difference in direction ofpolarization.

[0071] In the optical information recording/reproducing method of theinvention, the step of generating recording-specific reference light maygenerate recording-specific reference light having a spatially modulatedphase, and the step of generating reproduction-specific reference lightmay generate reproduction-specific reference light having a spatiallymodulated phase. In this case, the recording-specific reference lightand the reproduction-specific reference light may each have such amodulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of an optical axis of the opticalsystem for irradiating the information recording layer with therecording-specific reference light and the reproduction-specificreference light is not the same as the modulation pattern.

[0072] Other objects, features and advantages of the invention willbecome sufficiently clear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073]FIG. 1 is an explanatory diagram illustrating a configuration of apick-up of an optical information recording/reproducing apparatusaccording to an embodiment of the invention.

[0074]FIG. 2 is a block diagram illustrating a general configuration ofthe optical information recording/reproducing apparatus according to theembodiment of the invention.

[0075]FIG. 3 is an explanatory diagram for explaining polarized lightused in the embodiment of the invention.

[0076]FIG. 4 is an explanatory diagram illustrating a state of thepick-up during a servo operation in the embodiment of the invention.

[0077]FIG. 5 is an explanatory diagram illustrating a state of thepick-up during a recording operation in the embodiment of the invention.

[0078]FIG. 6 is an explanatory diagram illustrating a state of light inthe vicinity of the optical information recording medium during therecording operation in the embodiment of the invention.

[0079]FIG. 7 is an explanatory diagram illustrating an example of apattern of information light in the embodiment of the invention.

[0080]FIG. 8 is an explanatory diagram illustrating an example of amodulation pattern of recording-specific reference light in theembodiment of the invention.

[0081]FIG. 9 is an explanatory diagram illustrating a pattern which ispoint-symmetric to the modulation pattern shown in FIG. 8.

[0082]FIG. 10 is an explanatory diagram for explaining the principle ofrecording in the embodiment of the invention.

[0083]FIG. 11 is an explanatory diagram illustrating a state of thepick-up during a reproducing operation in the embodiment of theinvention.

[0084]FIG. 12 is an explanatory diagram for explaining the principle ofreproduction in the embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0085] Hereinafter, an embodiment of the invention will be described indetail with reference to the drawings.

[0086] First, with reference to FIG. 1 and FIG. 2, description will begiven of a configuration of an optical information recording/reproducingapparatus acting as an optical information recording apparatus and anoptical information reproducing apparatus according to the embodiment ofthe invention. FIG. 1 is an explanatory diagram illustrating aconfiguration of a pick-up of the optical informationrecording/reproducing apparatus according to the present embodiment.FIG. 2 is a block diagram illustrating a general configuration of theoptical information recording/reproducing apparatus according to theembodiment.

[0087] First, with reference to FIG. 1, description will be given of aconfiguration of an optical information recording medium used in thepresent embodiment. The optical information recording medium 1 of theembodiment comprises a disk-like transparent substrate 2 made ofpolycarbonate or the like, and an information recording layer 3, atransparent substrate 4, and a reflecting layer 5 that are arranged inthis order from the transparent substrate 2, on a side of thetransparent substrate 2 opposite from the light incident/emergent side.The transparent substrate 4 may be replaced with an air gap layer. Theinformation recording layer 3 is a layer in which information isrecorded through the use of holography, and is made of a hologrammaterial which varies, when irradiated with light, in its opticalcharacteristics such as refractive index, permittivity, and reflectance,depending on the intensity of the light. For example, hologram materialssuch as photopolymer HRF-600 (product name) manufactured by Dupont andphotopolymer ULSH-500 (product name) manufactured by Aprils may be used.The reflecting layer 5 is made of aluminum, for example. Incidentally,in the optical information recording medium 1, the information recordinglayer 3 and the reflecting layer 5 may be arranged next to each otherwithout the transparent substrate 4.

[0088] The surface of the reflecting layer 5 facing the transparentsubstrate 4 serves as a reflecting surface for reflecting light forrecording or reproducing information. Although not shown, a plurality ofaddress servo areas serving as positioning areas and extending linearlyin radial directions are provided at predetermined angular intervals onthe reflecting surface. Sections in the form of sectors between adjacentones of the address servo areas serve as data areas. In the addressservo areas, information for performing focus servo and tracking servounder a sampled servo system and address information are recorded inadvance in the form of emboss pits or the like. The focus servo can beperformed by using the reflecting surface of the reflecting layer 5. Forexample, wobble pits may be used as the information for performingtracking servo.

[0089] Next, the configuration of the optical informationrecording/reproducing apparatus according to the embodiment will bedescribed with reference to FIG. 2. The optical informationrecording/reproducing apparatus 10 has: a spindle 81 on which theoptical information recording medium 1 is mounted; a spindle motor 82for rotating the spindle 81; and a spindle servo circuit 83 forcontrolling the spindle motor 82 to keep the rotation speed of theoptical information recording medium 1 at a predetermined value. Theoptical information recording/reproducing apparatus 10 further has: apick-up 11 for irradiating the optical information recording medium 1with information light and recording-specific reference light to recordinformation therein, and irradiating the optical information recordingmedium 1 with reproduction-specific reference light to detectreproduction light to thereby reproduce information recorded in theoptical information recording medium 1; and a driving device 84 forallowing the pick-up 11 to move in a direction of the radius of theoptical information recording medium 1.

[0090] The optical information recording/reproducing apparatus 10further has: a detection circuit 85 for detecting a focus error signalFE, a tracking error signal TE and a reproduction signal RF from asignal outputted from the pick-up 11; and a focus servo circuit 86 forperforming focus servo by driving an actuator in the pick-up 11 based onthe focus error signal FE detected by the detection circuit 85 to movean objective lens in a direction of the thickness of the opticalinformation recording medium 1. The optical informationrecording/reproducing apparatus 10 further has: a tracking servo circuit87 for performing tracking servo by driving the actuator in the pick-up11 based on the tracking error signal TE detected by the detectioncircuit 85 to move the objective lens in a direction of the radius ofthe optical information recording medium 1; and a slide servo circuit 88for performing slide servo by controlling the driving device 84 based onthe tracking error signal TE and a command from a controller to bedescribed later to move the pick-up 11 in a direction of the radius ofthe optical information recording medium 1.

[0091] The optical information recording/reproducing apparatus 10further has: a signal processing circuit 89 for reproducing datarecorded in the data areas 7 of the optical information recording medium1 by decoding data outputted by a CCD array to be described later in thepick-up 11 and for reproducing a basic clock and determining addressesfrom the reproduction signal RF from the detection circuit 85; acontroller 90 for controlling the optical informationrecording/reproducing apparatus 10 as a whole; and an operating portion91 for supplying various instructions to the controller 90. Thecontroller 90 receives input of the basic clock and address informationoutputted by the signal processing circuit 89 and controls the pick-up11, the spindle servo circuit 83, the slide servo circuit 88 and thelike. The basic clock outputted by the signal processing circuit 89 isinputted to the spindle servo circuit 83. The controller 90 has a CPU(central processing unit), a ROM (read only memory) and a RAM (randomaccess memory), and the CPU executes programs stored in the ROM usingthe RAM as a work area to perform the functions of the controller 90.

[0092] A configuration of the pick-up 11 of the embodiment will now bedescribed with reference to FIG. 1. The pick-up 111 includes a lightsource device 12 that emits coherent linearly polarized laser light, anda collimator lens 13, a rotation-causing optical element 15, apolarization beam splitter 16, a phase spatial light modulator 17, abeam splitter 18, and a photodetector 19 that are arranged in this orderfrom the light source device 12 in a traveling direction of the lightemitted from the light source device 12.

[0093] The light source device 12 emits S-polarized or P-polarizedlinear light. The collimator lens 13 collimates the light emitted by thelight source device 12 to emit parallel beams thereof. Therotation-causing optical element 15 optically rotates the light emittedby the collimator lens 13 to emit light including S-polarized componentsand P-polarized components. S-polarized light refers to linear polarizedlight whose direction of polarization is perpendicular to the incidenceplane (plane of the drawing sheet of FIG. 1). P-polarized light refersto linear polarized light whose direction of polarization is parallel tothe incidence plane. For example, a half-wave plate or an opticalrotation plate is used as the rotation-causing optical element 15.

[0094] The polarization beam splitter 16 has a polarization beamsplitter surface 16 a that reflects the S-polarized components of thelight emergent from the rotation-causing optical element 15 andtransmits the P-polarized components thereof. The phase spatial lightmodulator 17 has a number of pixels arranged in a matrix, and is capableof spatially modulating the phase of light by selecting the phase ofemergent light pixel by pixel. A liquid crystal element may be used asthe phase spatial light modulator 17.

[0095] The beam splitter 18 has a beam splitter surface 18 a. Forexample, the beam splitter surface 18 a transmits 20% of the P-polarizedcomponents and reflects 80% of the same. The photodetector 19 is used tomonitor the quantity of reference light for performing automatic powercontrol (hereinafter referred to as APC) over the reference light. Alight-receiving portion of the photodetector 19 may be divided into aplurality of areas to allow adjustment of the intensity distribution ofthe reference light.

[0096] The pick-up 11 further has a polarization beam splitter 20, atwo-way split optical rotation plate (two-way split gyrator) 21 and aobjective lens 23 that are arranged in this order from the beam splitter18 in a direction in which the light from the light source device 12travels after being reflected by the beam splitter surface 18 a of thebeam splitter 18.

[0097] The polarization beam splitter 20 has a polarization beamsplitter surface 20 a for reflecting S-polarized components of lightincident thereon and for transmitting P-polarized components thereof.The polarization beam splitter 20 corresponds to the polarizationseparation means of the invention.

[0098] The two-way split optical rotation plate 21 has optical rotationplates 21L and 21R disposed on the left side and the right side,respectively, of the optical axis as viewed in FIG. 1. The opticalrotation plate 21R causes a −45° rotation of the direction ofpolarization, while the optical rotation plate 21L causes a +45°rotation of the direction of polarization. The two-way split opticalrotation plate 21 corresponds to the optical rotation means of theinvention.

[0099] The objective lens 23 faces toward the transparent substrate 2 ofthe optical information recording medium 1 when the optical informationrecording medium 1 is secured to the spindle 81. The pick-up 11 furtherhas an actuator (not shown) that is capable of moving the objective lens23 in a direction of the thickness of the optical information recordingmedium 1 and in a direction of the tracks.

[0100] The pick-up 11 further has a spatial light modulator 25, a beamsplitter 27, and a photodetector 28 that are arranged in this order fromthe polarization beam splitter 16 in a direction in which the light fromthe light source device 12 travels after being reflected by thepolarization beam splitter surface 16 a of the polarization beamsplitter 16.

[0101] The spatial light modulator 25 has a number of pixels arranged ina matrix, and is capable of generating information light that carriesinformation by spatially modulating light in terms of intensity byselecting a light-transmitting state or a light-blocking state for eachof the pixels. A liquid crystal element may be used as the spatial lightmodulator 25.

[0102] The beam splitter 27 has a beam splitter surface 27 a. Forexample, the beam splitter surface 27 a transmits 20% of S-polarizedcomponents and reflects 80% of the same. The photodetector 28 is used tomonitor the quantity of the information light to thereby perform APC onthe information light. The light-receiving portion of the photodetector28 may be divided into a plurality of areas to allow adjustment of theintensity distribution of the information light. Light that is incidenton the beam splitter 27 from the side of the spatial light modulator 25and reflected by the beam splitter surface 27 a is to be incident on thepolarization beam splitter 20.

[0103] The pick-up 11 further has a convex lens 29, a cylindrical lens30, and a four-way split photodetector 31 that are arranged in thisorder from the beam splitter 27, on a side of the beam splitter 27opposite to the polarization beam splitter 20. The four-way splitphotodetector 31 has four light-receiving portions divided by a divisionline that is parallel to a direction corresponding to the direction oftracks of the optical information recording medium 1 and a division linethat is orthogonal thereto. The cylindrical lens 30 is provided suchthat the central axis of the cylindrical surface thereof is at an angleof 45° to the division lines of the four-way split photodetector 31.

[0104] The pick-up 11 further has an imaging lens 32 and a CCD array 33that are arranged in this order from the beam splitter 18, on a side ofthe beam splitter 18 opposite to the polarization beam splitter 20. TheCCD array 33 corresponds to the detection means of the invention.

[0105] The pick-up 11 further has an APC circuit 46 connected to thephotodetector 19, and an APC circuit 47 connected to the photodetector28. The APC circuit 46 amplifies the output of the photodetector 19 togenerate a signal APC_(ref) used for APC to be performed on thereference light. The APC circuit 47 amplifies the output of thephotodetector 28 to generate a signal APC_(obj) used for APC to beperformed on the information light.

[0106] In order to adjust a ratio between the S-polarized components andP-polarized components of the light emergent from the rotation-causingoptical element 15, the pick-up 11 further has a motor 42, a gear 43 fortransmitting the rotation of an output axis of the motor 42 to therotation-causing optical element 15, and a driving circuit 48 fordriving the motor 42. The driving circuit 48 compares the respectivesignals APC_(ref) and APC_(obj) of APC circuits 46 and 47 with eachother, and drives the motor 42 so that the ratio between the S-polarizedcomponents and P-polarized components of the light emergent from therotation-causing optical element 15 is optimized.

[0107] The light source device 12, the phase spatial light modulator 17and the spatial light modulator 25 in the pick-up 11 are controlled bythe controller 90 shown in FIG. 2. The controller 90 holds informationon a plurality of modulation patterns for spatially modulating the phaseof light with the phase spatial light modulator 17. The operatingportion 91 allows selection of any one of the plurality of modulationpatterns. Then, the controller 90 supplies the information on themodulation pattern selected by itself or by the operating portion 91 tothe phase spatial light modulator 17 in accordance with predeterminedconditions. In accordance with the information on the modulation patternsupplied by the controller 90, the phase spatial light modulator 17spatially modulates the phase of light in the corresponding modulationpattern.

[0108] Now, with reference to FIG. 3, definitions will be given to terms“A-polarized light” and “B-polarized light” which will be used later inthis description. As shown in FIG. 3, A-polarized light is linearpolarized light obtained by rotating the direction of polarization ofthe S-polarized light by −45° or by rotating the direction ofpolarization of the P-polarized light by +45°, while B-polarized lightis linear polarized light obtained by rotating the direction ofpolarization of the S-polarized light by +45° or by rotating thedirection of polarization of the P-polarized light by −45°. Thedirections of polarization of the A-polarized light and B-polarizedlight are orthogonal to each other.

[0109] Servo, recording, and reproducing operations of the opticalinformation recording/reproducing apparatus according to the embodimentwill now be separately described in that order. The followingdescription also serves to describe the optical information recordingmethod, the optical information reproducing method, and the opticalinformation recording/reproducing method according to the embodiment.

[0110] The servo operation will now be described with reference to FIG.4. FIG. 4 is an explanatory diagram illustrating a state of the pick-up11 during the servo operation. During the servo operation, all thepixels of the spatial light modulator 25 are brought into a blockingstate. The phase spatial light modulator 17 is set such that lightpassing through each of the pixels thereof has the same phase as eachother. The output of light emitted by the light source device 12 is setto a low level suitable for reproduction. The controller 90 predicts thetiming at which light emergent from the objective lens 23 passes throughthe address servo areas based on a basic clock reproduced from areproduction signal RF, and maintains the foregoing setting while thelight emergent from the objective lens 23 passes through the addressservo areas.

[0111] The light emitted by the light source device 12 is collimated bythe collimator lens 13 and passes through the rotation-causing opticalelement 15 to be incident on the polarization beam splitter 16.S-polarized components of the light incident on the polarization beamsplitter 16 are reflected by the polarization beam splitter surface 16 aand are blocked by the spatial light modulator 25. P-polarizedcomponents of the light incident on the polarization beam splitter 16are transmitted by the polarization beam splitter surface 16 a and passthrough the phase spatial light modulator 17 to be incident on the beamsplitter 18. Part of the light incident on the beam splitter 18 isreflected by the beam splitter surface 18 a and passes through thepolarization beam splitter 20 to be incident on the two-way splitoptical rotation plate 21. Here, light that has passed through theoptical rotation plate 21R of the two-way split optical rotation plate21 becomes B-polarized light, while light that has passed through theoptical rotation plate 21L becomes A-polarized light. The light havingpassed through the two-way split optical rotation plate 21 is collectedby the objective lens 23, is projected onto the optical informationrecording medium 1, and converges to a minimum diameter on thereflecting surface of the optical information recording medium 1. Thislight is reflected by the reflecting surface, at which time it ismodulated by pits formed on the reflecting surface and returns to theobjective lens 23.

[0112] The return light from the optical information recording medium 1is collimated by the objective lens 23 and passes through the two-waysplit optical rotation plate 21 to become S-polarized light. That is,the light passing through the optical rotation plate 21R beforeimpinging on the information recording medium 1 is B-polarized light,and this light passes through the optical rotation plate 21L after beingreflected by the reflecting surface of the optical information recordingmedium 1 to become S-polarized light. On the other hand, the lightpassing through the optical rotation plate 21L before impinging on theinformation recording medium 1 is A-polarized light, and this lightpasses through the optical rotation plate 21R after being reflected bythe reflecting surface of the optical information recording medium 1 tobecome S-polarized light. Thus, the return light is reflected by thepolarization beam splitter surface 20 a of the polarization beamsplitter 20. This return light impinges on the beam splitter 27, andpart of the light is transmitted by the beam splitter surface 27 a andpasses through the convex lens 29 and the cylindrical lens 30sequentially to be detected by the four-way split photodetector 31.Based on the output of the four-way split photodetector 31, thedetection circuit 85 generates a focus error signal FE, a tracking errorsignal TE, and a reproduction signal RF. Based on these signals, focusservo and tracking servo are performed, along with reproduction of thebasic clock and determination of addresses.

[0113] Part of the light incident on the beam splitter 18 impinges onthe photodetector 19. Based on signals outputted by the photodetector19, the APC circuit 46 generates a signal APC_(ref). Then, APC isperformed based on the signal APC_(ref) such that the opticalinformation recording medium 1 is irradiated with a constant quantity oflight. Specifically, the driving circuit 48 drives the motor 42 toadjust the rotation-causing optical element 15 such that the signalAPC_(ref) equals a predetermined value. Alternatively, during the servooperation, APC may be performed by setting the rotation-causing opticalelement 15 such that light which has passed through the rotation-causingoptical element 15 has P-polarized components only, and by adjusting theoutput of the light source device 12. When the light-receiving portionof the photodetector 19 is divided into a plurality of areas and thephase spatial light modulator 17 is capable of also adjusting thequantity of light transmitted thereby, the light to be projected ontothe optical information recording medium 1 may be adjusted to have auniform intensity distribution by adjusting the quantity of lighttransmitted by each pixel of the phase spatial light modulator 17 basedon a signal outputted by each of the light-receiving portions of thephotodetector 19.

[0114] For the above-described setting for the servo operation, theconfiguration of the pick-up 11 is the same as that of a pick-up forrecording and reproduction on a typical optical disk. Therefore, theoptical information recording/reproducing apparatus of the embodimentallows recording and reproduction using a typical optical disk.

[0115] A recording operation will now be described with reference toFIG. 5 through FIG. 10. FIG. 5 is an explanatory diagram illustrating astate of the pick-up 11 during the recording operation. FIG. 6 is anexplanatory diagram illustrating a state of light in the vicinity of theoptical information recording medium 1 during the recording operation.FIG. 7 is an explanatory diagram illustrating an example of a pattern ofthe information light. FIG. 8 is an explanatory diagram illustrating anexample of a modulation pattern of the recording-specific referencelight. FIG. 9 is an explanatory diagram illustrating a pattern which ispoint-symmetric to the modulation pattern shown in FIG. 8. FIG. 10 is anexplanatory diagram for explaining the principle of recording.

[0116] During the recording operation, the spatial light modulator 25spatially modulates light passing therethrough by selecting atransmitting state (hereinafter also referred to as ON) or a blockingstate (hereinafter also referred to as OFF) pixel by pixel according toinformation to be recorded, thereby generating information light havingsuch a pattern as is shown in FIG. 7.

[0117] The phase spatial light modulator 17 spatially modulates thephase of light passing therethrough by selectively giving the light aphase difference of either 0 (rad) or π (rad) from a predeterminedreference phase pixel by pixel according to a predetermined modulationpattern, thereby generating recording-specific reference light having aspatially modulated phase.

[0118] The recording-specific reference light has such a modulationpattern that a pattern which is point-symmetric to the modulationpattern about the position of the optical axis of the optical system forirradiating the information recording layer 3 with therecording-specific reference light and the reproduction-specificreference light is not the same as the modulation pattern. FIG. 8 showsan example of such a modulation pattern. In FIG. 8, portions having aphase difference of 0 (rad) from the predetermined reference phase areshown as bright portions, while portions having a phase difference of π(rad) from the predetermined reference phase are shown as dark portions.FIG. 9 shows a pattern which is point-symmetric to the modulationpattern shown in FIG. 8. As can be seen, the pattern which ispoint-symmetric to the modulation pattern shown in FIG. 8 is not thesame as the original modulation pattern shown in FIG. 8.

[0119] The controller 90 supplies the information on the modulationpattern selected by itself or by the operating portion 91 to the phasespatial light modulator 17 in accordance with predetermined conditions.In accordance with the information on the modulation pattern supplied bythe controller 90, the phase spatial light modulator 17 spatiallymodulates the phase of the light passing therethrough.

[0120] The power of light emitted by the light source device 12 is setto reach high levels on a pulse basis suitable for recording. Thecontroller 90 predicts the timing at which the light emergent from theobjective lens 23 passes through the data areas based on the basic clockreproduced from the reproduction signal RF, and maintains the foregoingsetting while the light emergent from the objective lens 23 passesthrough the data areas. While the light emergent from the objective lens23 passes through the data areas, neither focus servo nor tracking servois performed and the objective lens 23 is fixed.

[0121] The light emitted by the light source device 12 is collimated bythe collimator lens 13 and passes through the rotation-causing opticalelement 15 to be incident on the polarization beam splitter 16.P-polarized components of the light incident on the polarization beamsplitter 16 are transmitted through the polarization beam splittersurface 16 a and pass through the phase spatial light modulator 17, atwhich time the light is spatially modulated in phase to becomerecording-specific reference light. The recording-specific referencelight is incident on the beam splitter 18. Part of therecording-specific reference light incident on the beam splitter 18 isreflected by the beam splitter surface 18 a and passes through thepolarization beam splitter 20 to impinge on the two-way split opticalrotation plate 21. Here, the recording-specific reference light that haspassed through the optical rotation plate 21R of the two-way splitoptical rotation plate 21 becomes B-polarized light, while therecording-specific reference light that has passed through the opticalrotation plate 21L becomes A-polarized light. The recording-specificreference light having passed through the two-way split optical rotationplate 21 is collected by the objective lens 23, is projected onto theoptical information recording medium 1, and converges to a minimumdiameter on the reflecting surface of the optical information recordingmedium 1.

[0122] On the other hand, S-polarized components of the light incidenton the polarization beam splitter 16 are reflected by the polarizationbeam splitter surface 16 a and pass through the spatial light modulator25, at which time the light is spatially modulated in accordance withthe information to be recorded, and thereby becomes information light.The information light is incident on the beam splitter 27. Part of theinformation light incident on the beam splitter 27 is reflected by thebeam splitter surface 27 a, and reflected by the beam splitter surface20 a of the polarization beam splitter 20, to impinge on the two-waysplit optical rotation plate 21. Here, the information light that haspassed through the optical rotation plate 21R of the two-way splitoptical rotation plate 21 becomes A-polarized light, while theinformation light that has passed through the optical rotation plate 21Lbecomes B-polarized light. The information light having passed throughthe two-way split optical rotation plate 21 is collected by theobjective lens 23, is projected onto the optical information recordingmedium 1, and converges to a minimum diameter on the reflecting surfaceof the optical information recording medium 1.

[0123] As shown in FIG. 6, according to the present embodiment, theinformation light and the recording-specific reference light areprojected coaxially onto one side of the information recording layer 3so as to converge on the reflecting surface.

[0124] The principle of recording of information according to thepresent embodiment will now be described with reference to FIG. 10. Theinformation light 51R that impinges on the information recording medium1 after having passed through the optical rotation plate 21R isA-polarized light. The recording-specific reference light 52L thatimpinges on the information recording medium 1 after having passedthrough the optical rotation plate 21L is also A-polarized light. TheA-polarized recording-specific reference light 52L is reflected by thereflecting surface 5 a of the information recording medium 1, and passesthrough the same area of the information recording layer 3 as theA-polarized information light 51R does. The light 51L and the light 52Rinterfere with each other to form an interference pattern because theirdirections of polarization coincide with each other. On the other hand,the A-polarized information light 51R is reflected by the reflectingsurface 5 a of the information recording medium 1, and passes throughthe same area of the information recording layer 3 as the A-polarizedrecording-specific reference light 52L does. The light 51L and the light52R also interfere with each other to form an interference patternbecause their directions of polarization coincide with each other. Thus,the interference pattern resulting from the interference between theA-polarized information light 51R yet to impinge on the reflectingsurface 5 a and the A-polarized recording-specific reference light 52Lreflected by the reflecting surface 5 a, and the interference patternresulting from the interference between the A-polarizedrecording-specific reference light 52L yet to impinge on the reflectingsurface 5 a and the A-polarized information light 51R reflected by thereflecting surface 5 a, are volumetrically recorded in the informationrecording layer 3.

[0125] Likewise, The information light 51L that impinges on theinformation recording medium 1 after having passed through the opticalrotation plate 21L is B-polarized light. The recording-specificreference light 52R that impinges on the information recording medium 1after having passed through the optical rotation plate 21R is alsoB-polarized light. The B-polarized recording-specific reference light52R is reflected by the reflecting surface 5 a of the informationrecording medium 1, and passes through the same area of the informationrecording layer 3 as the B-polarized information light 51L does. Thelight 51L and the light 52R interfere with each other to form aninterference pattern because their directions of polarization coincidewith each other. On the other hand, the B-polarized information light51L is reflected by the reflecting surface 5 a of the informationrecording medium 1, and passes through the same area of the informationrecording layer 3 as the B-polarized recording-specific reference light52R does. The light 51L and the light 52R also interfere with each otherto form an interference pattern because their directions of polarizationcoincide with each other. Thus, the interference pattern resulting fromthe interference between the B-polarized information light 51L yet toimpinge on the reflecting surface 5 a and the B-polarizedrecording-specific reference light 52R reflected by the reflectingsurface 5 a, and the interference pattern resulting from theinterference between the B-polarized recording-specific reference light51L yet to impinge on the reflecting surface 5 a and the B-polarizedinformation light 52R reflected by the reflecting surface 5 a, arevolumetrically recorded in the information recording layer 3.

[0126] In FIG. 6, the reference number 50 represents areas of theinformation recording layer 3 where the interference patterns resultingfrom the interference between the information light and therecording-specific reference light are recorded in the above-describedmanner.

[0127] The information light 51R that has passed through the opticalrotation plate 21R and the information light 51L that has passed throughthe optical rotation plate 21L do not interfere with each other becausethey differ in direction of polarization by 90°. Likewise, therecording-specific reference light 52R that has passed through theoptical rotation plate 21R and the recording-specific reference light52L that has passed through the optical rotation plate 21L do notinterfere with each other because they differ in direction ofpolarization by 90°.

[0128] According to the present embodiment, a plurality of pieces ofinformation can be recorded in an identical location of the informationrecording layer 3 on a multiplex basis through phase-encodingmultiplexing by changing the modulation pattern of the phase of therecording-specific reference light for each piece of the information tobe recorded.

[0129] As shown in FIG. 5, part of the recording-specific referencelight incident on the beam splitter 18 impinges on the photodetector 19.Based on signals outputted by the photodetector 19, the APC circuit 46generates the signal APC_(ref). On the other hand, part of theinformation light incident on the beam splitter 27 impinges on thephotodetector 28. Based on signals outputted by the photodetector 28,the APC circuit 47 generates the signal APC_(obj). Based on the signalsAPC_(ref) and APC_(obj), APC is performed so that the ratio between theintensities of the recording-specific reference light and theinformation light projected onto the optical information recordingmedium 1 is set at an optimum value. Specifically, the driving circuit48 compares the signals APC_(ref) and APC_(obj) with each other, anddrives the motor 42 to adjust the rotation-causing optical element 15 soas to obtain a desired ratio. When the light-receiving portion of thephotodetector 19 is divided into a plurality of areas and the phasespatial light modulator 17 is capable of also adjusting the quantity oflight transmitted thereby, the light to be projected onto the opticalinformation recording medium 1 may be adjusted to have a uniformintensity distribution by adjusting the quantity of light transmitted byeach pixel of the phase spatial light modulator 17 based on a signaloutputted by each of the light-receiving portions of the photodetector19. Likewise, when the light-receiving portion of the photodetector 28is divided into a plurality of areas and the spatial light modulator 25is capable of also adjusting the quantity of light transmitted thereby,the information light to be projected onto the optical informationrecording medium 1 may be adjusted to have a uniform intensitydistribution by adjusting the quantity of light transmitted by eachpixel of the spatial light modulator 25 based on a signal outputted byeach of the light-receiving portions of the photodetector 28.

[0130] In the present embodiment, APC is performed based on the sum ofthe signals APC_(ref) and APC_(obj) so that the total intensity of therecording-specific reference light and the information light achieves anoptimum value. Methods for controlling the total intensity of therecording-specific reference light and the information light includecontrolling over a peak value of the output of the light source device12 and controlling over an emission pulse width and a time-courseprofile of the intensity of emitted light in the case where the light isemitted in the form of pulses.

[0131] Description will now be given of the reproducing operation withreference to FIG. 11 and FIG. 12. FIG. 11 is an explanatory diagramillustrating a state of the pick-up 11 during the reproducing operation.FIG. 12 is an explanatory diagram for explaining the principle ofreproduction.

[0132] During the reproducing operation, all pixels of the spatial lightmodulator 25 are brought into a blocking state. The phase spatial lightmodulator 17 spatially modulates the phase of light passing therethroughby selectively giving the light a phase difference of either 0 (rad) orπ (rad) from a predetermined reference phase pixel by pixel according toa predetermined modulation pattern, thereby generatingreproduction-specific reference light having a spatially modulatedphase. Here, the reproduction-specific reference light is given amodulation pattern which is the same as the modulation pattern of therecording-specific reference light used for recording the information tobe reproduced, or which is point-symmetric to the modulation pattern ofthe recording-specific reference light about the position of the opticalaxis of the optical system for irradiating the information recordinglayer 3 with the recording-specific reference light and thereproduction-specific reference light. In either case, thereproduction-specific reference light has such a modulation pattern thata pattern which is point-symmetric to the modulation pattern about theposition of the optical axis of the optical system for irradiating theinformation recording layer 3 with the recording-specific referencelight and the reproduction-specific reference light is not the same asthe modulation pattern.

[0133] The light emitted by the light source device 12 is collimated bythe collimator lens 13 and passes through the rotation-causing opticalelement 15 to be incident on the polarization beam splitter 16.S-polarized components of the light incident on the polarization beamsplitter 16 are reflected by the polarization beam splitter surface 16 aand are blocked by the spatial light modulator 25. P-polarizedcomponents of the light incident on the polarization beam splitter 16are transmitted by the polarization beam splitter surface 16 a and passthrough the phase spatial light modulator 17, at which time the light isspatially modulated in phase to become reproduction-specific referencelight. The reproduction-specific reference light is incident on the beamsplitter 18. Part of the reproduction-specific reference light incidenton the beam splitter 18 is reflected by the beam splitter surface 18 aand passes through the polarization beam splitter 20 to impinge on thetwo-way split optical rotation plate 21. Here, the reproduction-specificreference light that has passed through the optical rotation plate 21Rof the two-way split optical rotation plate 21 becomes B-polarizedlight, while the reproduction-specific reference light that has passedthrough the optical rotation plate 21L becomes A-polarized light. Thereproduction-specific reference light having passed through the two-waysplit optical rotation plate 21 is collected by the objective lens 23,is projected onto the optical information recording medium 1, andconverges to a minimum diameter on the reflecting surface of the opticalinformation recording medium 1.

[0134] The positioning (servo control) of the reproduction-specificreference light with respect to the optical information recording medium1 can be performed in the same manner as the positioning of therecording-specific reference light and the information light in therecording operation.

[0135] The principle of reproduction of information in the presentembodiment will now be described with reference to FIG. 12. Thereproduction-specific reference light 61R that impinges on theinformation recording medium 1 after having passed through the opticalrotation plate 21R is B-polarized light. On the other hand, thereproduction-specific reference light 61L that impinges on theinformation recording medium 1 after having passed through the opticalrotation plate 21L is A-polarized light. In the information recordinglayer 3, the reproduction-specific reference light yet to be reflectedby the reflecting surface 5 a generates reproduction light which travelsaway from the reflecting surface 5 a, and the reproduction-specificreference light reflected by the reflecting surface 5 a generatesreproduction light which travels toward the reflecting surface 5 a. Thereproduction light traveling away from the reflecting surface 5 a isemitted as-is from the optical information recording medium 1. Thereproduction light traveling toward the reflecting surface 5 a isreflected by the reflecting surface 5 a and emitted from the opticalinformation recording medium 1.

[0136] The reproduction light is collimated by the objective lens 23 andthen impinges on the two-way split optical rotation plate 21. Here, thereproduction light 62R to impinge on the optical rotation plate 21R ofthe two-way split optical rotation plate 21 is B-polarized light beforeimpinging on the optical rotation plate 21R, and becomes P-polarizedlight after passing through the optical rotation plate 21R. On the otherhand, the reproduction light 62L to impinge on the optical rotationplate 21L of the two-way split optical rotation plate 21 is A-polarizedlight before impinging on the optical rotation plate 21L, and becomesP-polarized light after passing through the optical rotation plate 21L.Thus, the reproduction light having passed through the two-way splitoptical rotation plate 21 becomes P-polarized light over the entirecross section of the beam thereof.

[0137] The reproduction light having passed through the two-way splitoptical rotation plate 21 is incident on the polarization beam splitter20 and transmitted by the polarization beam splitter surface 20 a to beincident on the beam splitter 18. Part of the reproduction lightincident on the beam splitter 18 is transmitted by the beam splittersurface 18 a and passes through the imaging lens 32 to impinge on theCCD array 33.

[0138] On the CCD array 33 is formed an image of the ON/OFF patterncaused by the spatial light modulator 25 in the recording operation, sothat information is reproduced by detecting this pattern. When aplurality of pieces of information are recorded in the informationrecording layer 3 on a multiplex basis by changing modulation patternsof the recording-specific reference light, among the plurality of piecesof information, the one corresponding to the modulation pattern of thereproduction-specific reference light is only reproduced. In the casewhere the reproduction-specific reference light has the same modulationpattern as that of the recording-specific reference light used forrecording the information to be reproduced, the reproduction light has apattern which is inverted (mirror pattern) from the pattern of theinformation light used in the recording operation. In the case where thereproduction-specific reference light has a modulation pattern which ispoint-symmetric to the modulation pattern of the recording-specificreference light used for recording the information to be reproduced, thereproduction light has the same pattern as that of the information lightused in the recording operation. In either case, it is possible toreproduce information based on the pattern of the information light.

[0139] The reproduction-specific reference light 61R incident on theinformation recording medium 1 after having passed through the opticalrotation plate 21R is reflected by the reflecting surface 5 a andemitted from the optical information recording medium 1. The light thenpasses through the optical rotation plate 21L and is converted intoS-polarized return light. On the other hand, the reproduction-specificreference light 61L incident on the information recording medium 1 afterhaving passed through the optical rotation plate 21L is reflected by thereflecting surface 5 a and emitted from the optical informationrecording medium 1. The light then passes through the optical rotationplate 21R and is converted into S-polarized return light. Thus, thereturn light having passed through the two-way split optical rotationplate 21 becomes S-polarized light over the entire cross section of thebeam thereof. Since the return light impinges on the polarization beamsplitter 20 to be reflected by the polarization beam splitter surface 20a, it does not impinge on the CCD array 33.

[0140] Part of the reproduction-specific reference light incident on thebeam splitter 18 impinges on the photodetector 19. Based on signalsoutputted by the photodetector 19, the APC circuit 46 generates a signalAPC_(ref). APC is performed based on the signal APC_(ref) so that theoptical information recording medium 1 is irradiated with a constantquantity of the reproduction-specific reference light. Specifically, thedriving circuit 48 drives the motor 42 to adjust the rotation-causingoptical element 15 so that the signal APC_(ref) equals a predeterminedvalue. Alternatively, during the reproducing operation, APC may beperformed by setting the rotation-causing optical element 15 such thatlight which has passed through the rotation-causing optical element 15has P-polarized components only, and by adjusting the output of thelight source device 12. When the light-receiving portion of thephotodetector 19 is divided into a plurality of areas and the phasespatial light modulator 17 is capable of also adjusting the quantity oflight transmitted thereby, the light to be projected onto the opticalinformation recording medium 1 may be adjusted to have a uniformintensity distribution by adjusting the quantity of light transmitted byeach pixel of the phase spatial light modulator 17 based on a signaloutputted by each of the light-receiving portions of the photodetector19.

[0141] As described in the foregoing, according to the presentembodiment, to record information, the information light and therecording-specific reference light are projected coaxially onto one sideof the information recording layer 3 such that they converge on thereflecting surface.

[0142] Furthermore, to record information, each of therecording-specific reference light having a first direction ofpolarization (P-polarized) and the information light having a seconddirection of polarization (S-polarized) that is different from the firstdirection of polarization (P-polarized) is optically rotated by thetwo-way split optical rotation plate 21 serving as the optical rotationmeans in directions different between respective half areas of the crosssection of the beam thereof. Thus, for each of the information light andthe recording-specific reference light, the direction of polarization isset to be different between the respective half areas of the crosssection of the beam thereof such that the direction of polarization ofthe information light yet to impinge on the reflecting surface coincideswith that of the recording-specific reference light reflected by thereflecting surface, and the direction of polarization of therecording-specific reference light yet to impinge on the reflectingsurface coincides with that of the information light reflected by thereflecting surface. As a result, in the information recording layer 3,an interference pattern resulting from interference between theinformation light yet to impinge on the reflecting surface and therecording-specific reference light reflected by the reflecting surfaceis recorded, and also an interference pattern resulting frominterference between the recording-specific reference light yet toimpinge on the reflecting surface and the information light reflected bythe reflecting surface is recorded.

[0143] On the other hand, to reproduce information, thereproduction-specific reference light is projected onto the informationrecording layer 3 so as to converge on the reflecting surface. Theprojection of the reproduction-specific reference light and thecollection of the reproduction light are performed on one side of theinformation recording layer 3, and the reproduction-specific referencelight and the reproduction light are arranged coaxially.

[0144] Furthermore, to reproduce information, the reproduction-specificreference light having the first direction of polarization (P-polarized)is optically rotated by the two-way split optical rotation plate 21 indirections different between respective half areas of the cross sectionof the beam thereof, converted into reproduction-specific referencelight having different directions of polarization for the respectivehalf areas, and projected onto the information recording layer 3.Reproduction light and return light resulting from thereproduction-specific reference light reflected by the reflectingsurface are each optically rotated by the two-way split optical rotationplate 21 in directions different between the respective half areas, andconverted into reproduction light having the first direction ofpolarization (P-polarized) over the entire cross section of the beamthereof and return light having the second direction of polarization(S-polarized) over the entire cross section of the beam thereof. It isthereby possible to separate the reproduction light and the return lightfrom each other by the polarization beam splitter 20 serving as thepolarization separation means, and consequently, it is possible toimprove the SN ratio of the reproduced information.

[0145] According to the embodiment, the information light can carryinformation using the entire cross section of the beam thereof.Likewise, the reproduction light can also carry information using theentire cross section of the beam thereof.

[0146] From the foregoing, the embodiment makes it possible to recordand reproduce information through the use of holography and to achieve acompact configuration of the optical system for recording andreproduction without causing a reduction in the amount of information.

[0147] Furthermore, in the embodiment, the recording-specific referencelight and the reproduction-specific reference light each have such amodulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of the optical axis of the opticalsystem for irradiating the information recording layer 3 with therecording-specific reference light and the reproduction-specificreference light is not the same as the modulation pattern. Therefore,according to the embodiment, when reproducing information it is possibleto prevent simultaneous occurrences of a pattern the same as the patternof the information light used for recording the information and a mirrorpattern thereof.

[0148] The present invention is not limited to the foregoing embodimentand may be modified in various ways. For example, in the foregoingembodiment, the address information and the like are recorded in advancein the form of emboss pits on the address servo areas of the opticalinformation recording medium 1. However, the address information and thelike may be recorded in the following manner without providing theemboss pits in advance. In this case, the optical information recordingmedium 1 shall be configured such that the information recording layer 3and the reflecting layer 5 are next to each other without thetransparent substrate 4. Then, in the address servo areas of thisoptical information recording medium 1, the information recording layer3 is irradiated with laser light of high output selectively at a portioncloser to the reflecting layer 5. The portion is thereby selectivelychanged in refractive index so that address information and the like arerecorded to perform formatting.

[0149] In the embodiment, information is recorded on a multiplex basisby phase-encoding multiplexing. However, the present invention alsocovers the cases where multiplex recording by phase-encodingmultiplexing is not conducted.

[0150] As described in the foregoing, in the optical informationrecording apparatus or the optical information recording method of theinvention, the information light and the recording-specific referencelight are projected coaxially onto one side of the information recordinglayer so as to converge on the reflecting surface. In the informationrecording layer, the direction of polarization of the information lightyet to impinge on the reflecting surface coincides with that of therecording-specific reference light reflected by the reflecting surface,so that an interference pattern resulting from the interferencetherebetween is recorded. On the other hand, the direction ofpolarization of the recording-specific reference light yet to impinge onthe reflecting surface coincides with that of the information lightreflected by the reflecting surface, so that an interference patternresulting from the interference therebetween is recorded. Furthermore,in the invention, the information light can carry information using theentire cross section of the beam thereof. The invention therefore makesit possible to record information through the use of holography and toachieve compact configuration of the optical system for recordingwithout causing a reduction in the amount of information.

[0151] According to the optical information reproducing apparatus or theoptical information reproducing method of the invention, thereproduction-specific reference light is projected onto the informationrecording layer so as to converge on the reflecting surface. Theprojection of the reproduction-specific reference light and thecollection of the reproduction light are performed on one side of theinformation recording layer, and the reproduction-specific referencelight and the reproduction light are arranged coaxially. Furthermore, inthe invention, the reproduction-specific reference light having apredetermined first direction of polarization is optically rotated indirections different between respective half areas of a cross section ofthe beam of the light, and thereby converted into reproduction-specificreference light having directions of polarization different between therespective areas to irradiate the information recording layer therewith,and reproduction light and return light are each optically rotated indirections different between the respective areas and thereby convertedinto reproduction light having the first direction of polarization overthe entire cross section of the beam thereof and return light having asecond direction of polarization which is different from the firstdirection of polarization over the entire cross section of the beamthereof. Furthermore, in the invention, the information light can carryinformation using the entire cross section of the beam thereof, andlikewise, the reproduction light can also carry information using theentire cross section of the beam thereof. The invention therefore makesit possible to reproduce information through the use of holography andto achieve compact configuration of the optical system for reproductionwithout causing a reduction in the amount of information.

[0152] According to the optical information recording/reproducingapparatus or the optical information recording/reproducing method of theinvention, it is possible to record and reproduce information throughthe use of holography and to achieve compact configuration of theoptical system for recording and reproduction without causing areduction in the amount of information, through the same operation asthat of the optical information recording apparatus or the opticalinformation recording method described above and the same operation asthat of the optical information reproducing apparatus or the opticalinformation reproducing method described above.

[0153] It is apparent from the foregoing description that the inventionmay be carried out in various modes and may be modified in various ways.It is therefore to be understood that within the scope of equivalence ofthe appended claims the invention may be practiced in modes other thanthe foregoing best modes.

1. An optical information recording apparatus for recording informationin an optical information recording medium having an informationrecording layer in which information is recorded through the use ofholography and one side of which is irradiated with light for recordingor reproducing information, and a reflecting surface disposed on theother side of the information recording layer, the apparatus comprising:information light generation means for generating information light thatcarries information; recording-specific reference light generation meansfor generating recording-specific reference light; and a recordingoptical system for irradiating the information recording layer with theinformation light generated by the information light generation meansand the recording-specific reference light generated by therecording-specific reference light generation means such that theinformation is recorded in the information recording layer in the formof an interference pattern resulting from interference between theinformation light and the recording-specific reference light, whereinthe recording optical system projects the information light and therecording-specific reference light coaxially onto the one side of theinformation recording layer such that they converge on the reflectingsurface, and the recording optical system causes each of the informationlight and the recording-specific reference light to have directions ofpolarization that are different between respective half areas of a crosssection of a beam thereof such that the direction of polarization of theinformation light yet to impinge on the reflecting surface coincideswith that of the recording-specific reference light reflected by thereflecting surface, and the direction of polarization of therecording-specific reference light yet to impinge on the reflectingsurface coincides with that of the information light reflected by thereflecting surface.
 2. An optical information recording apparatusaccording to claim 1, wherein the recording optical system has opticalrotation means for optically rotating light passing therethrough indirections different between the respective areas, and opticallyrotates, with the optical rotation means, each of the recording-specificreference light having a predetermined first direction of polarizationand the information light having a second direction of polarizationdifferent from the first direction of polarization to make thedirections of polarization different between the respective areas.
 3. Anoptical information recording apparatus according to claim 1, whereinthe recording-specific reference light generation means generatesrecording-specific reference light having a spatially modulated phase.4. An optical information recording apparatus according to claim 3,wherein the recording-specific reference light has such a modulationpattern that a pattern which is point-symmetric to the modulationpattern about the position of an optical axis of the optical system forirradiating the information recording layer with the recording-specificreference light is not the same as the modulation pattern.
 5. An opticalinformation recording method for recording information in an opticalinformation recording medium having an information recording layer inwhich information is recorded through the use of holography and one sideof which is irradiated with light for recording or reproducinginformation, and a reflecting surface disposed on the other side of theinformation recording layer, the method comprising: the step ofgenerating information light that carries information; the step ofgenerating recording-specific reference light; and the recording step inwhich the information recording layer is irradiated with the informationlight and the recording-specific reference light such that theinformation is recorded in the information recording layer in the formof an interference pattern resulting from interference between theinformation light and the recording-specific reference light, wherein inthe recording step, the information light and the recording-specificreference light are projected coaxially onto the one side of theinformation recording layer such that they converge on the reflectingsurface, and in the recording step, each of the information light andthe recording-specific reference light is made to have directions ofpolarization that are different between respective half areas of a crosssection of a beam thereof such that the direction of polarization of theinformation light yet to impinge on the reflecting surface coincideswith that of the recording-specific reference light reflected by thereflecting surface, and the direction of polarization of therecording-specific reference light yet to impinge on the reflectingsurface coincides with that of the information light reflected by thereflecting surface.
 6. An optical information recording method accordingto claim 5, wherein, in the recording optical step, each of therecording-specific reference light having a predetermined firstdirection of polarization and the information light having a seconddirection of polarization different from the first direction ofpolarization is optically rotated in directions different between therespective areas to make the directions of polarization differentbetween the respective areas.
 7. An optical information recording methodaccording to claim 5, wherein the step of generating recording-specificreference light generates recording-specific reference light having aspatially modulated phase.
 8. An optical information recording methodaccording to claim 7, wherein the recording-specific reference light hassuch a modulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of an optical axis of the opticalsystem for irradiating the information recording layer with therecording-specific reference light is not the same as the modulationpattern.
 9. An optical information reproducing apparatus for reproducinginformation through the use of holography from an optical informationrecording medium having an information recording layer in whichinformation is recorded through the use of holography and one side whichis irradiated with light for recording or reproducing information, and areflecting surface disposed on the other side of the informationrecording layer, the information being recorded in the informationrecording layer based on information light and recording-specificreference light that are projected coaxially onto the one side of theinformation recording layer such that they converge on the reflectingsurface, in the form of an interference pattern resulting frominterference between the information light yet to impinge on thereflecting surface and the recording-specific reference light reflectedby the reflecting surface and an interference pattern resulting frominterference between the recording-specific reference light yet toimpinge on the reflecting surface and the information light reflected bythe reflecting surface, the apparatus comprising: reproduction-specificreference light generation means for generating reproduction-specificreference light; a reproducing optical system for irradiating theinformation recording layer with the reproduction-specific referencelight generated by the reproduction-specific reference light generationmeans and for collecting reproduction light generated at the informationrecording layer when irradiated with the reproduction-specific referencelight; and detection means for detecting the reproduction lightcollected by the reproducing optical system, wherein the reproducingoptical system projects the reproduction-specific reference light ontothe information recording layer to allow it to converge on thereflecting surface, such that the irradiation with thereproduction-specific reference light and the collection of thereproduction light are performed on the one side, and that thereproduction-specific reference light and the reproduction light arearranged coaxially, and the reproducing optical system has opticalrotation means for optically rotating light passing therethrough indirections different between respective half areas of a cross section ofa beam of the light, and optically rotates, with the optical rotationmeans, the reproduction-specific reference light having a predeterminedfirst direction of polarization to convert the same intoreproduction-specific reference light having directions of polarizationdifferent between the respective areas to irradiate the informationrecording layer therewith, and optically rotates, with the opticalrotation means, the reproduction light and return light resulting fromthe reproduction-specific reference light reflected by the reflectingsurface to convert them into reproduction light having the firstdirection of polarization over an entire cross section of a beam thereofand return light having a second direction of polarization differentfrom the first direction of polarization over an entire cross section ofa beam thereof.
 10. An optical information reproducing apparatusaccording to claim 9, wherein the reproducing optical system further haspolarization separation means for separating the reproduction lighthaving passed through the optical rotation means and the return lighthaving passed through the optical rotation means from each otherdepending on a difference in direction of polarization.
 11. An opticalinformation reproducing apparatus according to claim 9, wherein thereproduction-specific reference light generation means generatesreproduction-specific reference light having a spatially modulatedphase.
 12. An optical information reproducing apparatus according toclaim 11, wherein the reproduction-specific reference light has such amodulation pattern that a pattern which is point-symmetric to themodulation pattern about the position of an optical axis of the opticalsystem for irradiating the information recording layer with thereproduction-specific reference light is not the same as the modulationpattern.
 13. An optical information reproducing method for reproducinginformation through the use of holography from an optical informationrecording medium having an information recording layer in whichinformation is recorded through the use of holography and one side ofwhich is irradiated with light for recording or reproducing information,and a reflecting surface disposed on the other side of the informationrecording layer, the information being recorded in the informationrecording layer based on information light and recording-specificreference light that are projected coaxially onto the one side of theinformation recording layer such that they converge on the reflectingsurface, in the form of an interference pattern resulting frominterference between the information light yet to impinge on thereflecting surface and the recording-specific reference light reflectedby the reflecting surface and an interference pattern resulting frominterference between the recording-specific reference light yet toimpinge on the reflecting surface and the information light reflected bythe reflecting surface, the method comprising: the step of generatingreproduction-specific reference light; the reproducing step in which theinformation recording layer is irradiated with the reproduction-specificreference light generated by the reproduction-specific reference lightgeneration means, and reproduction light generated at the informationrecording layer when irradiated with the reproduction-specific referencelight is collected; and the step of detecting the reproduction light,wherein in the reproducing step, the reproduction-specific referencelight is projected onto the information recording layer so as toconverge on the reflecting surface such that the irradiation with thereproduction-specific reference light and the collection of thereproduction light are performed on the one side, and that thereproduction-specific reference light and the reproduction light arearranged coaxially, and in the reproducing step, thereproduction-specific reference light having a predetermined firstdirection of polarization is optically rotated in directions differentbetween respective half areas of a cross section of a beam thereof, andthereby converted into reproduction-specific reference light havingdirections of polarization different between the respective areas toirradiate the information recording layer therewith, and thereproduction light and return light resulting from thereproduction-specific reference light reflected by the reflectingsurface are each optically rotated in directions different between therespective areas and thereby converted into reproduction light havingthe first direction of polarization over an entire cross section of abeam thereof and return light having a second direction of polarizationdifferent from the first direction of polarization over an entire crosssection of a beam thereof.
 14. An optical information reproducing methodaccording to claim 13, wherein the reproducing step separates thereproduction light that has been optically rotated and the return lightthat has been optically rotated from each other depending on adifference in direction of polarization.
 15. An optical informationreproducing method according to claim 13, wherein the step of generatingreproduction-specific reference light generates reproduction-specificreference light having a spatially modulated phase.
 16. An opticalinformation reproducing method according to claim 15, wherein thereproduction-specific reference light has such a modulation pattern thata pattern which is point-symmetric to the modulation pattern about theposition of an optical axis of the optical system for irradiating theinformation recording layer with the reproduction-specific referencelight is not the same as the modulation pattern.
 17. An opticalinformation recording/reproducing apparatus for recording information inan optical information recording medium having an information recordinglayer in which information is recorded through the use of holography andone side of which is irradiated with light for recording or reproducinginformation, and a reflecting surface disposed on the other side of theinformation recording layer, and for reproducing information from theoptical information recording medium, the apparatus comprising:information light generation means for generating information light thatcarries information; recording-specific reference light generation meansfor generating recording-specific reference light; reproduction-specificreference light generation means for generating reproduction-specificreference light; a recording/reproducing optical system for, to recordinformation, irradiating the information recording layer with theinformation light generated by the information light generation meansand the recording-specific reference light generated by therecording-specific reference light generation means such thatinformation is recorded in the information recording layer in the formof an interference pattern resulting from interference between theinformation light and the recording-specific reference light, and, toreproduce information, irradiating the information recording layer withthe reproduction-specific reference light generated by thereproduction-specific reference light generation means and collectingreproduction light generated at the information recording layer whenirradiated with the reproduction-specific reference light; and detectionmeans for detecting the reproduction light collected by therecording/reproducing optical system, wherein the recording/reproducingoptical system has optical rotation means for optically rotating lightpassing therethrough in directions different between respective halfareas of a cross section of a beam of the light, to record information,the recording/reproducing optical system projects the information lightand the recording-specific reference light coaxially onto the one sideof the information recording layer such that they converge on thereflecting surface, to record information, the recording/reproducingoptical system optically rotates, with the optical rotation means, eachof the recording-specific reference light having a predetermined firstdirection of polarization and the information light having a seconddirection of polarization different from the first direction ofpolarization to cause each of the information light and therecording-specific reference light to have directions of polarizationdifferent between the respective areas, such that the direction ofpolarization of the information light yet to impinge on the reflectingsurface coincides with that of the recording-specific reference lightreflected by the reflecting surface, and the direction of polarizationof the recording-specific reference light yet to impinge on thereflecting surface coincides with that of the information lightreflected by the reflecting surface, to reproduce information, therecording/reproducing optical system projects the reproduction-specificreference light onto the information recording layer to allow it toconverge on the reflecting surface, such that the irradiation with thereproduction-specific reference light and the collection of thereproduction light are performed on the one side, and that thereproduction-specific reference light and the reproduction light arearranged coaxially, and to reproduce information, therecording/reproducing optical system optically rotates, with the opticalrotation means, the reproduction-specific reference light having thefirst direction of polarization to convert the same intoreproduction-specific reference light having directions of polarizationdifferent between the respective areas to irradiate the informationrecording layer therewith, and optically rotates, with the opticalrotation means, the reproduction light and return light resulting fromthe reproduction-specific reference light reflected by the reflectingsurface to convert them into reproduction light having the firstdirection of polarization over an entire cross section of a beam thereofand return light having a second direction of polarization differentfrom the first direction of polarization over an entire cross section ofa beam thereof.
 18. An optical information recording/reproducingapparatus according to claim 17, wherein the recording/reproducingoptical system further has polarization separation means for separatingthe reproduction light having passed through the optical rotation meansand the return light having passed through the optical rotation meansfrom each other depending on a difference in direction of polarization.19. An optical information recording/reproducing apparatus according toclaim 17, wherein the recording-specific reference light generationmeans generates recording-specific reference light having a spatiallymodulated phase, and the reproduction-specific reference lightgeneration means generates reproduction-specific reference light havinga spatially modulated phase.
 20. An optical informationrecording/reproducing apparatus according to claim 19, wherein therecording-specific reference light and the reproduction-specificreference light each have such a modulation pattern that a pattern whichis point-symmetric to the modulation pattern about the position of anoptical axis of the optical system for irradiating the informationrecording layer with the recording-specific reference light and thereproduction-specific reference light is not the same as the modulationpattern.
 21. An optical information recording/reproducing method forrecording information in an optical information recording medium havingan information recording layer in which information is recorded throughthe use of holography and one side of which is irradiated with light forrecording or reproducing information, and a reflecting surface disposedon the other side of the information recording layer, and forreproducing information from the optical information recording medium,the method comprising: the step of generating information light thatcarries information; the step of generating recording-specific referencelight; the recording step in which the information recording layer isirradiated with the information light and the recording-specificreference light such that the information is recorded in the informationrecording layer in the form of an interference pattern resulting frominterference between the information light and the recording-specificreference light; the step of generating reproduction-specific referencelight; the reproducing step in which the information recording layer isirradiated with the reproduction-specific reference light, andreproduction light generated at the information recording layer whenirradiated with the reproduction-specific reference light is collected;and the step of detecting the reproduction light, wherein in therecording step, the information light and the recording-specificreference light are projected coaxially onto the one side of theinformation recording layer such that they converge on the reflectingsurface, in the recording step, each of the recording-specific referencelight having a predetermined first direction of polarization and theinformation light having a second direction of polarization differentfrom the first direction of polarization is optically rotated indirections different between respective half areas of a cross section ofa beam thereof to cause each of the information light and therecording-specific reference light to have directions of polarizationdifferent between the respective areas, such that the direction ofpolarization of the information light yet to impinge on the reflectingsurface coincides with that of the recording-specific reference lightreflected by the reflecting surface, and the direction of polarizationof the recording-specific reference light yet to impinge on thereflecting surface coincides with that of the information lightreflected by the reflecting surface, in the reproducing step, thereproduction-specific reference light is projected onto the informationrecording layer so as to converge on the reflecting surface, such thatthe irradiation with the reproduction-specific reference light and thecollection of the reproduction light are performed on the one side, andthat the reproduction-specific reference light and the reproductionlight are arranged coaxially, and in the reproducing step, thereproduction-specific reference light having a predetermined firstdirection of polarization is optically rotated in directions differentbetween respective half areas of a cross section of a beam thereof, andthereby converted into reproduction-specific reference light havingdirections of polarization different between the respective areas toirradiate the information recording layer therewith, and thereproduction light and return light resulting from thereproduction-specific reference light reflected by the reflectingsurface are each optically rotated in directions different between therespective areas and thereby converted into reproduction light havingthe first direction of polarization over an entire cross section of abeam thereof and return light having a second direction of polarizationdifferent from the first direction of polarization over an entire crosssection of a beam thereof.
 22. An optical informationrecording/reproducing method according to claim 21, wherein thereproducing step separates the reproduction light that has beenoptically rotated and the return light that has been optically rotatedfrom each other depending on a difference in direction of polarization.23. An optical information recording/reproducing method according toclaim 21, wherein the step of generating recording-specific referencelight generates recording-specific reference light having a spatiallymodulated phase, and the step of generating reproduction-specificreference light generates reproduction-specific reference light having aspatially modulated phase.
 24. An optical informationrecording/reproducing method according to claim 23, wherein therecording-specific reference light and the reproduction-specificreference light each have such a modulation pattern that a pattern whichis point-symmetric to the modulation pattern about the position of anoptical axis of the optical system for irradiating the informationrecording layer with the recording-specific reference light and thereproduction-specific reference light is not the same as the modulationpattern.